Vehicle tires, particularly pneumatic or semi-pneumatic tires, are often reinforced by means of cords consisting of twisted or cabled brass and/or zinc-coated steel filaments. Such tire cord is often composed of a high carbon-steel filament having a very thin layer of brass, such as alpha brass, sometimes with the brass coating itself also having a thin zinc layer thereon, or a ternary alloy addition, such as cobalt or nickel. The cord may be monofilament although it is more normally prepared by cabling or stranding several filaments together. Generally, the steel filament is prepared by coating with brass, such as by electroplating, then cold drawn and stranded and/or cabled to form the cord.
Plated steel wire cords are generally subject to corrosion of the steel substrate and oxidation of the brass coating, particularly if improperly handled or stored prior to incorporation into a rubber composite which is ultimately shaped to a molded article such as a pneumatic tire. Corrosion and oxidation can also be caused from other external agents or elements in an environment where the cord is a reinforcement such as in a rubber composite. Such corrosion and oxidation can result in poor adhesion between the cords and rubber which, in turn, can result in a failure of the reinforcement in the rubber composite or can cause degradation of a good adhesive bond during service life of the composite.
Clean, untreated brass coated steel wire will normally have a reasonably good initial adhesion to the adjacent rubber. However, the adhesion typically will drop with time, particularly with aging due to heat, stress and/or chemical degradation or corrosion effects. Various additives described in the literature have in certain instances shown improved initial and aged adhesion. Yet such additives have often not proved entirely satisfactory either due to required complexities in their preparation or the mixed results realized from their use. Indeed, some types of aging would show improved adhesion and others apparently no improvement. It is therefore desirable that an agent, or agents, be found which protect(s) the bare metallic surface and does not adversely affect initial adhesion to any great degree, while at the same time, improving aged adhesion of a vulcanized composite. Further, it it particularly desired that such adhesion enhancing process be relatively simple and economical.
Various chemical reagents have been proposed and/or used to treat such coated wire for the purpose of protecting against corrosion and oxidation. For example, benzotriazole, tolyltriazole and naphthyltriazole, have been taught to be useful. Such reagents have sometimes been taught to be applied as a coating to the surface of a filament or cord by various methods, such as by immersing the wire in a water solution of the reagent, by treating the wire with the reagent in its molten form, or by exposing the wire to the reagent in its vapor phase.
Although the mechanism is not clearly understood, apparently such reagents physcially or chemically combine with the wire or wire coating to offer protection against oxidation and/or corrosion while often maintaining adhesion to a rubber substrate. Perhaps the reagent coating on the wire affects the sulfur/copper bond which might be formed between the wire and the adjacent rubber in a rubber composite which is reinforced with the wire.
It is important to appreciate, that reagents are continually being sought for the purpose of preventing or retarding oxidation and/or corrosion of the wire, particularly while the wire is in the form of reinforcement in a sulfur-cured rubber composite. In these regards, it is considered that it is not enough that reagents which are known or taught or thought to be corrosion inhibitors be arbitrarily chosen. This is because that such reagent, while it may be thought to be useful as a corrosion inhibitor, must also not degrade the adhesion between the cord and the rubber. Indeed, it is desired that such reagents actually enhance the cord to rubber bonding or adhesion.
For example, if it were only desired to prevent the corrosion of the wire, then it could be treated with the material such as vasoline, mineral oil or lacquer. However, it is surely readily recognized that such materials would be expected to seriously inhibit adhesion of the cord to rubber.
Therefore, it is desired to provide a treatment for steel filament or cord which has been previously metal or metal alloy plated such as with alloys containing predominantly brass and/or zinc, and to the resultant treated article. It is further desired to form a composite of rubber and such filament or cord as a reinforcement. It is also desired to provide articles containing such reinforcements such as pneumatic and semi-pneumatic tires, as well as industrial hose and industrial belts such as power transmission and conveyor belts.